[BUG/ISSUE] Negative area diagnostic in global 2x2.5 standalone simulation

[LukeFakes]

I’ve been running tests with the HEMCO standalone at 2x2.5 recently and came across an issue that leads to negative areas in the grid box area diagnostic at the most northern latitude.

This was happening with the standard standalone run directory setup, and seems to be a result of a missing “YEDGE” argument in the default standalone grid file (HEMCO_sa_Grid.2x25.rc). The resulting global simulation looks like this:

For a 4x5 global simulation, if the YEDGE argument was removed, the same problem occurred, so this is likely not resolution-dependent. I haven’t looked at whether it happens for non-global standalone runs but would assume not based on a look at hcoi_standalone_mod.F90. I think it’s happening because when YEDGE is not provided, the model calculates a latitude beyond 90.0, leading to a negative value for SIN_DELTA

Also, the description on the wiki suggests the XEDGE and YEDGE arguments are optional, but this might not be the case, at least for global runs while this is a problem.

HEMCO_sa_Grid.2x25.txt
HEMCO_sa_Grid.2x25.wYEDGE.txt

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